The present invention relates to a deployment system for deploying a moveable wing surface, such as a slat or flap, from a main wing section.
Various mechanisms have been proposed for deploying slats and flaps on aircraft wings, including paired track systems, Kruger flap systems and swing arm systems. The present invention relates to a swing arm system, for example of the general type described in International patent application No: PCT/NZ95/00096.
It has been shown to be beneficial in deployment systems to have an arrangement that achieves a configuration during takeoff wherein the slat is deployed and rotated relative to the main wing to a first extent such that there is no gap between the deployed slat and the leading edge of the main wing, and a configuration during landing wherein the slat is deployed and rotated to a second, greater, extent such that a slot is formed between the trailing edge of the slat and the leading edge of the wing (for example, see U.S. Pat. No. 4,399,970). Most wings taper from root to tip, and variable camber devices should mimic this taper to give full benefits along the length of the wing.
In prior art swing arm slat deployment systems such as that described in PCT/NZ95/00096, normally only one of the swing arms is driven, the undriven swing arm simply following the movement of the driven arm owing to its connection to that arm through the slat. This avoids mechanical stresses in the slats and the swing arms which might otherwise occur, for example when the slat and the wing experience different degrees of thermal expansion during flight. However, the arrangement suffers from the disadvantage that the undriven arm is not closely controlled, which can result in a step being left between the slat and the main wing section when the slat is in a stowed position.
However, if both swing arms are driven, the mechanism becomes susceptible to mechanical stress and could also under certain circumstances become jammed with one swing arm slightly in front of the line that passes through the pivot joints and the other swing arm slightly behind that line. This risk may be heightened when, for example, the slat and the wing experience different amounts of thermal expansion, or when the mechanical components in the slat mechanism are worn or do not meet required manufacturing tolerances. Locking of the swing arms could prevent the slat from deploying fully or cause it to become stuck in a partially-deployed position with potentially dangerous results.
A slat deployment system is described in GB 2362363 that addresses some of these issues. That system includes a slat that is connected to a main wing by first and second arm assemblies. Each arm assembly includes a swing arm that is pivotally attached to the main wing and upper and lower connector assemblies connecting the slat to the swing arm. The first and second arm assemblies are very similar: however, they differ in that the upper joint of the second arm assembly includes a lost motion mechanism. The slat is deployed from the main wing section by a drive system that drives both the first and second arm assemblies. The lost motion mechanism included in the second arm assembly reduces the potential for jamming by compensating for thermal expansion and contraction of the slat without transmitting stresses to the main wing.
The deployment system described in GB 2362363 provides a way of meeting the desired slat configurations for take off and landing described above and overcoming the problems associated with systems where only one of the arm assemblies is driven. In particular, it is the arrangement of the swing arms that defines the extent of deployment of the slat and the interaction of the upper and lower connector assemblies that causes the slat to rotate and hence change its angle of attack. However, that system is considered to be overly complex and lack mechanical robustness.
In mechanical systems used on aircraft simplicity is paramount. For example, with deployment systems having multiple arms with many bearings, rigging of the system is difficult, initial costs are high, maintenance is expensive, and the possibility of system failure increases. With all deployment systems it is necessary to make sure that any linkage mechanism does not get into a kinematic arrangement where it becomes locked. Deployment systems also need to be rigid in all conditions to prevent flutter and rapid wear of joints, and they need to handle loads efficiently and relay them to the main wing structure.